The present invention relates to a tire vulcanizer, and more particularly to an improved opening/closing and centering device in a tire vulcanizer including a long-stroke cylinder for vertically moving an upper mold relative to a lower mold.
In such a tire vulcanizer of the above-mentioned type, the upper mold is required to be maintained in parallel to the lower mold and be centered with a high accuracy. To meet such a requirement, there has been proposed a tire vulcanizer as disclosed in Japanese Patent Laid-open Publication No. 61-134210, for example. The construction of the prior art vulcanizer is schematically shown in FIGS. 7 and 8. Referring to these figures, a lower mold 102 is fixed to a mold support 105 connected through a press cylinder 106 to a press frame 107. A pair of long-stroke cylinders 119 are mounted at right and left side portions of a top frame 108. A pair of piston rods 118 of the long-stroke cylinders 119 are connected to a pressure plate 117 fixed to an upper mold 101. The upper mold 101 is vertically moved to be opened and closed relative to the lower mold 102 by operating the piston rods 118 of the long-stroke cylinders 119. A guide column 109 is connected at its lower end to the pressure plate 117 at the central position thereof. During the vertical movement of the upper mold 101, the guide column 109 is guided by the top frame 108 to be vertically moved. The guide column 109 is formed on its outer circumferential surface with a pair of vertical guide ridges 110 each having a pair of vertical guide surfaces defining a given angle. The top frame 108 is provided with four upper guide rollers and four lower guide rollers 111 rotationally contacting the guide surfaces of the guide ridges 110. A stop jaw 114 with a locking cylinder for locking a closed condition of the upper mold 101 is provided on the top frame 108, and a stop nut 113 abutting against the stop jaw 114 is adjustably mounted on the guide column 109.
However, the opening/closing and centering means in the above-mentioned conventional vulcanizer has the following problems. First, the two long-stroke cylinders 119 are mounted to the top frame 108 at the right and left portions thereof, and the pressure plate 117 is vertically moved by lifting and lowering the two piston rods 118 of the long-stroke cylinders 119. Accordingly, it is difficult to tune both the cylinders 119, with the result that there will arise an error in levelness of the pressure plate 117, to cause an error in parallelism between the upper mold 101 and the lower mold 102.
Secondly, the centering means for the pressure plate 117 is constructed of the guide surfaces of the guide ridges 110 formed on the outer circumferential surface of the guide column 109 fixed at the central position of the pressure plate 117 and the guide rollers 111 rotationally contacting the guide surfaces of the guide ridges 110. However, a mechanical gap of each guide roller 111 at the central position of the pressure plate 117 is magnified at the outer circumferential portion of the circular pressure plate 117. Therefore, the centering of the pressure plate 117 with a high accuracy is difficult, causing a low registerability between the upper mold 101 and the lower mold 102.